The heterogeneous flooring and wall coverings market segment includes textile and plastic coverings. The heterogeneous coverings segment is distinguished from the homogeneous coverings segment (which includes materials such as linoleum) in that the heterogeneous segment refers to multilayer covering constructions involving different materials. In the heterogeneous resilient cushion flooring and wall covering market segment, there is a need for improved ecological solutions as alternatives to plasticized polyvinyl chloride (PVC) coverings and, to some extent, for alternatives to conventional textile coverings. The ecological concerns respecting the heterogeneous PVC covering segment pertain to recyclability or energy recovery, volatile organic content levels, and the use of heavy metal stabilizers and inorganic fillers. The ecological concerns pertaining to textile coverings include inhibition of or barrier against microorganism growth.
Heterogeneous foamed PVC flooring and wall coverings have been extremely popular due their simple installation and low cost. However, a great deal of their popularity is also owed to their attractive performance properties which include sound insulation, walking and standing comfort and print-design versatility. Minimum performance requirements in the segment include an EN433 indentation recovery (normalized) of greater than or equal to 90 and a DIN53455 elongation of greater than or equal to 150 percent.
Typical foamed PVC covering construction includes a PVC-plastisol based covering. The plastisol typically consists of PVC particles, plasticizer, heavy metal additives and inorganic filler. The covering layer is formed in a spreading process by laying-down the plastisol on a fabric or release paper substrate and subsequently curing the plastisol. The use of a fabric substrate such as fleece (as opposed to a release paper substrate) provides an intermediate material layer which confers enhanced dimensional stability to the cured covering.
The PVC covering layer is typically manufactured using a calendaring or roll mill process. In such processes, rigid PVC is formulated with plasticizers and heavy metal stabilizers. The use of heavy metal stabilizers (e.g., dilauryl tin distearate or carboxylates of barium and cadmium, barium and zinc or calcium and zinc) is especially important in these melt processes to avoid undo degradation of the polyvinyl chloride polymer.
However, whether manufactured using a spreading process or a calendaring process, in order to avoid an excessive number of seams or joints when installed, foamed PVC coverings are typically manufactured as endless webs having widths up to 4 or 5 meters. This width requirement is generally considered to significantly limit the possible products and/or processes available for providing suitable alternatives for foamed PVC coverings. See, for example, the disclosure by Oppermann et al. in U.S. Pat. No. 5,407,617 at Col. 1, lines 32-36, the disclosure of which is incorporated herein by reference. In particular, known processes for manufacturing crosslinked thermoplastic foams are said to be limited to widths of about 2 meters due to die width limitations. See, U.S. Pat. No. 5,407,617 at Col. 2, lines 8-28.
To overcome the perceived limitations of using established thermoplastic foaming processes, and thereby provide a PVC-free covering, Oppermann et al. describes a covering constructed from an acrylic wear layer and a thermoplastic foam backing. The thermoplastic foam backing disclosed by Oppermann et al. is made using a powder sintering process wherein the thermoplastic is formulated with a conventional blowing agent, cryogenically ground to a fine mesh powder, then sintered or scattered to 4-5 meters and finally foamed at about 120 to about 200.degree. C. However, powder sintering is relatively slow and in general is not considered to be conducive to high production rates. Also, acrylic wear layers such as described by Oppermann et al. are considered to exhibit mediocre scratch and abrasion resistance and the acrylate emulsions from which the acrylic layer is derived is also considered to be fairly expensive.
Urethane foamed backings with good wear resistance properties are also known wherein foaming is accomplished mechanically by air injection. However, urethane systems are fairly expensive and are not susceptible to foam inhibition. Moreover, there is no realistic opportunity to provide a substantially complete urethane covering to facilitate easy recyclability.
Hence, there is a need for a PVC-free resilient foam cushion flooring and wall covering product that meets the performance attributes of known heterogeneous coverings based on PVC. Such a product should be manufacturable at widths of at least 4 meters using low cost processing methods common to the heterogeneous covering segment.